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andrewwalker27
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PostPosted: Tue Jun 30, 2020 8:06 pm    Post subject: Ryzen experimental kernel risks Reply with quote

I'm interested in using the Ryzen kernel options but as they require the experimental use flag I'm a bit apprehensive, has anyone tried them out? I'm not using my machine for anything critical, and I'm already running ~amd64, but I'd like to know if they are reasonably stable to play with.
Anyone had any experience with them by any chance?
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NeddySeagoon
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PostPosted: Tue Jun 30, 2020 8:19 pm    Post subject: Reply with quote

andrewwalker27,

That's what backups, or snapshots are for.
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those that do backups
those that have never had a hard drive fail.
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saboya
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PostPosted: Tue Jun 30, 2020 8:55 pm    Post subject: Reply with quote

I compile the kernel with AMD Zen 2 processor family. I've using this for several months with no issues.
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kajzer
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PostPosted: Wed Jul 01, 2020 1:48 pm    Post subject: Reply with quote

It's safe, more important question is are there any benefits choosing for example znver2 as a processor family over "AMD/Athlon64..."
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Anon-E-moose
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PostPosted: Wed Jul 01, 2020 2:05 pm    Post subject: Reply with quote

kajzer wrote:
It's safe, more important question is are there any benefits choosing for example znver2 as a processor family over "AMD/Athlon64..."


For the kernel, I don't think it makes that much difference between generic x86_64 and znver2. For applications it can make a significant difference.
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kajzer
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PostPosted: Wed Jul 01, 2020 2:19 pm    Post subject: Reply with quote

Anon-E-moose wrote:
For the kernel, I don't think it makes that much difference between generic x86_64 and znver2. For applications it can make a significant difference.


Sure, I think OP was thinking about the kernel.
I could be wrong though.
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Goverp
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PostPosted: Wed Jul 01, 2020 6:12 pm    Post subject: Reply with quote

I've used the hack to achieve a similar effect:
Code:
KCFLAGS="-march=native" make -j24

for some time. It still works on my desktop machine (which is znver2), but it's recently started failing to compile on my laptop (bdver4) box, fails with "Error 255 in kernel 5.7 compiling arch/x86/events/amd/ibs.o",.
For now I'm using the nearest standard equivalent. I expect the problem will be cured when there's a gcc update. It's possible the "experimental" patches do something more intelligent than simply "-march=native", but I've not tried.
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kajzer
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PostPosted: Wed Jul 01, 2020 10:47 pm    Post subject: Reply with quote

Goverp wrote:
It's possible the "experimental" patches do something more intelligent than simply "-march=native", but I've not tried.


It's just "-march=native"
It's like that for every other cpu, I mean there's nothing more to it than what you would set in make.conf for 'march'
For znver2 it's just znver2 as well, etc.

You can check it anyway by extracting '/var/db/repos/gentoo/distfiles/genpatches-5.7-7.experimental.tar.xz' and looking at '5012_enable-cpu-optimizations-for-gcc91.patch'
Maybe I'm missing something :)
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Anon-E-moose
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PostPosted: Thu Jul 02, 2020 9:57 am    Post subject: Reply with quote

Sometimes march native works and sometimes it doesn't

For my oid fx cpu, it would crash and burn every time I used native (it was using piledriver)
it only worked when I set the cpu to bulldozer (previous gen) that worked fine, so I just left it like that, while I had that system installed.

Now, with the ryzen I still don't use native, I set it specifically for the cpu znver2 in this case.
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Juippisi
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PostPosted: Thu Jul 02, 2020 1:25 pm    Post subject: Re: Ryzen experimental kernel risks Reply with quote

andrewwalker27 wrote:
I'm interested in using the Ryzen kernel options but as they require the experimental use flag I'm a bit apprehensive, has anyone tried them out? I'm not using my machine for anything critical, and I'm already running ~amd64, but I'd like to know if they are reasonably stable to play with.
Anyone had any experience with them by any chance?


You can audit the experimental patches here:
https://dev.gentoo.org/~mpagano/genpatches/trunk/5.7/
They're the >=5000 ones.
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Goverp
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PostPosted: Fri Jul 03, 2020 8:24 am    Post subject: Reply with quote

Aha! Reading the optimization patch, I note a warning comment not to use "-march=native" with bdver4 cpus. That explains my problem, at least.
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